/*
 * Copyright [2013-2021], Alibaba Group Holding Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.calcite.rel.metadata;

import org.apache.calcite.plan.RelOptCost;
import org.apache.calcite.plan.volcano.RelSubset;
import org.apache.calcite.plan.volcano.VolcanoPlanner;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.util.BuiltInMethod;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Default implementations of the
 * {@link BuiltInMetadata.LowerBoundCost}
 * metadata provider for the standard algebra.
 */
public class RelMdLowerBoundCost implements MetadataHandler<BuiltInMetadata.LowerBoundCost> {

    public static final RelMetadataProvider SOURCE =
        ReflectiveRelMetadataProvider.reflectiveSource(
            new RelMdLowerBoundCost(), BuiltInMethod.LOWER_BOUND_COST.method);

    //~ Constructors -----------------------------------------------------------

    protected RelMdLowerBoundCost() {}

    //~ Methods ----------------------------------------------------------------

    @Override public MetadataDef<BuiltInMetadata.LowerBoundCost> getDef() {
        return BuiltInMetadata.LowerBoundCost.DEF;
    }

    public @Nullable RelOptCost getLowerBoundCost(RelSubset subset,
                                                  RelMetadataQuery mq, VolcanoPlanner planner) {

        if (planner.isLogical(subset)) {
            // currently only support physical, will improve in the future
            return null;
        }

        return subset.getWinnerCost();
    }

    public @Nullable RelOptCost getLowerBoundCost(RelNode node,
                                                  RelMetadataQuery mq, VolcanoPlanner planner) {
        if (planner.isLogical(node)) {
            // currently only support physical, will improve in the future
            return null;
        }

        RelOptCost selfCost = mq.getNonCumulativeCost(node);
        if (selfCost != null && selfCost.isInfinite()) {
            selfCost = null;
        }
        for (RelNode input : node.getInputs()) {
            RelOptCost lb = mq.getLowerBoundCost(input, planner);
            if (lb != null) {
                selfCost = selfCost == null ? lb : selfCost.plus(lb);
            }
        }
        return selfCost;
    }
}
